System and Method for Variation of the Pitch Angle Position of Rotor Blades of a Wind Energy Installation

ABSTRACT

A system for variation of the pitch angle position of rotor blades of a wind energy installation includes drive units, closed-loop control devices, and system control connections. The drive units are in each case individually associated with the rotor blades. The closed-loop control devices are in each case individually associated with the drive units. The system control connections are switchable by switching means. By way of the system control connections, in the event of a failure or a malfunction of at least one closed-loop control device a drive unit which is associated with the at least one closed-loop control device is operated in parallel with and at the same time as another drive unit, by means of a closed-loop control device which is associated with the other drive unit.

The present invention relates to a system and a method for altering the pitch of rotor blades of a wind turbine, in which drive units individually associated with each of the rotor blades and regulating devices individually associated with each of the drive units are provided.

PRIOR ART

Modern wind turbines operate according to the lift principle, where the individual rotor blades generate lift when acted upon by the wind, in a similar manner to an aircraft wing. The wind turbines are usually designed as so-called high-speed rotors and generally have several (for example, two or three) rotor blades.

Blade adjustment mechanisms (so-called pitch systems) are provided in such wind turbines so that the pitch of the rotor blades can be altered. The primary aim of the pitch adjustment is to regulate the output and speed of the rotor by influencing the lift generated in each case. Moreover, the rotor can be halted, by moving the rotor blades into the so-called feathered position in which there is no longer any torque acting on the axis of the rotor. The power coefficient, and thus the turbine output, are directly linked to the position of the rotor blades relative to the wind direction or to the plane of rotation of the turbine. The power output by the turbine is directly influenced by adjusting the rotor blades about their longitudinal axis. It is possible to protect a wind turbine from overload in the event of excessively strong wind by reducing or eliminating the lift.

In general, the rotor blades are adjusted independently of one another by drive units individually associated with each of them and with corresponding regulating devices. In other words, each rotor blade is provided with its own regulating device that operates independently of the regulating devices for the other rotor blades. The target values for the individual regulating devices are set by a superordinate control center, for example as a function of the wind speed.

In the case of adjustable rotor blades, all the blades need to be adjusted as synchronously as possible. Different positions of individual rotor blades result in an uneven distribution of aerodynamic force on the rotor and hence in aerodynamic imbalances that entail an excessive mechanical load on the turbine. Drives usually used in corresponding adjustment systems are for example based on brushless electromotors. However, the latter are only partly fail-safe because, inter alia, of the complex regulating systems required for their operation. Measures must therefore be taken in order to enable the turbine to continue to operate securely or be shut down in the event of failure or malfunction.

In conventional wind turbines, in the event of a fault in the regulating system of a drive unit, the turbine is immediately shut down in order to prevent overloading as a result of unsymmetrical blade pitches. However, this immediate shutting down entails a loss of revenue as maintenance is required in the case of each failure before the turbine can operate again.

In DE 10 2007 006 966 A1 it is proposed, in the event of failure of a regulating device, to activate the motor which has the failed regulating device using the regulating device of another motor, alternately with this other motor. However, a permanent switchover is required to do this, which increases the load on power switches (contactors) that correspondingly need to be provided, as a result of which asynchronous adjustment can cause asymmetries in the blade pitches and can entail low adjustment dynamics. A similar system, but which has the same disadvantages, is described in EP 1 664 527 B1.

Against this background, there is thus a need for a fail-safe design of systems for altering the pitch of wind turbine rotor blades.

SUMMARY OF THE INVENTION

According to the invention, a system and a method are proposed for altering the pitch of rotor blades of a wind turbine, in which drive units individually associated with each of the rotor blades and regulating devices individually associated with each of the drive units are provided, having the features of the independent patent claims. Advantageous embodiments are the subject of the subclaims and the following description.

ADVANTAGES OF THE INVENTION

The measures according to the invention include, in the event of a failure or in the event of a malfunction of the regulating device of the drive unit for a rotor blade, regulating this drive unit by a regulating device of another rotor blade. In contrast to the prior art, two drive units are hereby activated in parallel and simultaneously by a single regulating device (for example, a correspondingly regulated inverter). The invention thus proposes a direct parallel connection of the drive units in the case of a fault. The permanent switchover that is required according to the prior art with the redundant activation is hereby reduced and the loading of contactors that correspondingly need to be provided thus prevented. Because switchover times are no longer necessary, asymmetries in the blade positions are reduced and the adjustment dynamics are increased.

The invention thus offers the great advantage, relative to the prior art, that after the switchover is complete, both the first and the second drive are simultaneously activated. While a switchover takes place only when a fault occurs in the case of this simultaneous activation and the system then remains in the corresponding state, in the prior art a permanent switchover is required in the case of alternating activation. The lifetime of the contactors used can thus be lengthened and advantages ensue in terms of the number of switching cycles. Moreover, the downtimes of the contactors and brakes used only need to be taken into account once. Because the drives are not regularly braked, as is the case for each switchover procedure in the case of alternating activation, it is easier to track the target value for the pitch.

Although parallel activation of two drives by a regulating device is described in the context of the present application, it should be stressed that, even in the event of two or more regulating devices failing, the drives associated with the latter can be activated by another (intact) regulating device, if the corresponding power features have been provided.

A (more or less) identical pitch of the rotor blades is achieved by the frequency (and accordingly the speed of the motors) being preset, for example by a U/f controller.

No significant losses occur in the adjustment dynamics when the motors are connected in parallel, as long as the maximum current of the respective inverter is not exceeded in a regulating device that performs the activation as a result of the parallel connection. If a corresponding inverter does not have corresponding power reserves, adjustment dynamics may be reduced accordingly.

The proposed systems can be implemented using both asynchronous motors and synchronous motors.

In the case of synchronous motors, it is advantageously possible to prevent the risk that may exist of a rotor displacement angle of 90° being exceeded when the load torque exceeds the pull-out torque that can be achieved by the voltage and frequency at the motor (i.e. the motor “tilts”) by monitoring the rotor displacement angle using a motor model. If too large a rotor displacement angle is detected hereby, the dynamics of the system or the drives can be reduced so that the torque that needs to be delivered by a motor, and hence the rotor displacement angle, can be reduced again.

In the case of asynchronous motors, instead of the rotor displacement angle, a difference occurs in the speeds of mechanical rotors and an electrical field. As a result of this difference, known as “slip”, in the case of different load torques and despite identical voltage and frequency, two asynchronous motors deliver different torques without there being any risk of “tilting”. There is, however, a small difference in speed between the motors.

When a load is applied, deviations that increase over time in the pitches of rotor blades can therefore be observed (the pitches “diverge”). The reason for this is the different load torques of the motors of the respective drive units. Depending on the load torque and a detected pitch of a first axis, the target value for the speed of the second axis too is formed in a regulating device that activates both drives in the event of a fault. However, because the two drives are subject to different load torques, they will have correspondingly different angular speeds.

Differences in the pitch, that in particular result therefrom, of the rotor blades associated with the motors can advantageously be reduced by synchronizing the pitch when a determined threshold value for the difference in pitch is reached. To do this, the “leading” motor is advantageously stopped (“blocked”) by a braking device, the “lagging” motor is moved until the two motors have the same angle again (or until the difference falls below a threshold value that needs to be provided correspondingly). The two motors are then moved in parallel again. To do this, the angular position of both motors is advantageously determined by sensors.

The braking device used is advantageously an electromechanical brake that decelerates the motor when there is no current (with the braking circuit open). Simultaneously, the motor phases are hereby advantageously opened so that the decelerated motor is prevented from being overloaded. Corresponding switch means (for example in the form of contactor circuits) therefore advantageously need to be provided in the motor and braking circuits.

Other advantages and embodiments of the invention are apparent from the description and the attached drawings.

It should be understood that the abovementioned features and those that will be explained below can be used not only in the combinations stated in each case but also in combinations or in isolation without going beyond the scope of the present invention.

The invention is illustrated schematically in the drawings with the aid of exemplary embodiments and is described in detail below with reference to the drawings.

DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic view of a rotor blade with a pitch adjustment device according to the prior art associated with the latter.

FIG. 2 a shows a schematic view of a system with two pitch adjustment devices according to the prior art illustrated.

FIG. 2 b shows a system with two pitch adjustment devices for rotor blades according to a preferred embodiment of the invention illustrated.

FIG. 3 shows a flow diagram of a method according to a preferred embodiment of the invention.

In the following figures, identical elements or those with the same function have the same reference numbers and are not explained again for the sake of clarity.

A rotor blade with an associated pitch adjustment device according to the prior art is shown schematically in FIG. 1. The arrangement as a whole is denoted by 10. Essential components of the arrangement are a rotor blade 1 in the form of a hollow body, a drive unit 2 in the form of an electromotor, and a regulating device 3 associated with the drive unit 2. The drive unit 2 is connected via a gearbox 4 to a spur gear 5 that meshes with a toothed element 6 on the inside of the rotor blade 1. A torque can be introduced into the rotor blade 1 via the drive unit 2 and the gearbox 4 by means of the spur gear 5 in accordance with the regulating device 3. The rotor blade 1 is mounted in a blade bearing 7 that ensures the adjustment of the rotor blade 1 about its axis via the spur gear 5. Also provided is a superordinate control system 9 in the form of an operating management system that is connected to the regulating device 3 via an activating connection 8 and ensures that all the adjustment devices deliver an identical rotor blade position. The superordinate control system 9 can be connected to other superordinate elements that deliver requirements for the rotor position, for example based on wind strength.

A system with two adjustment devices for altering the pitch of rotor blades 1 is shown in FIG. 2 a and labeled 100 as a whole. The system 100 has two drive units 21, 22 that are each associated with corresponding rotor blades 1. Although only two adjustment devices are shown in the figure, it should be understood that the system can similarly also be used in turbines with more than two rotor blades. The drive units 21, 22 have a motor M and a brake B associated with the motor M. A motor can be decelerated by the brake B for example, as described above, as a result of which the blade position can be set and asynchronous rotor blade positions can be synchronized.

The drive units 21, 22 are each associated with regulating devices 31, 32 and connected to the latter via activating connections 311, 312, 321, 322 in the form of activating lines. The activating connections 311, 321 here each deliver the operating voltages provided by an inverter to the motors M. The brakes B are activated via the activating connections 312 and 322. Corresponding switch elements can be provided to switch the brakes B. As already explained in connection with FIG. 1, the individual adjustment devices are in contact with a superordinate control system 9 via an activating connection 8.

It can be seen in FIG. 2 a that, in the event of one of the regulating devices 31, 32 according to the prior art failing, it is no longer possible to adjust a corresponding blade pitch because the corresponding motor M and/or the corresponding brake B can no longer be activated. As explained, however, it is known in the prior art to provide means that make it possible, in the event of one of the regulating devices 31, 32 failing, to activate the respective other motors M in alternating fashion with the actually associated motor M. As explained, however, significant disadvantages follow from this, as a result of the switchover procedures and/or the downtimes caused by the switchover procedures.

A system formed in accordance with the present invention is shown in FIG. 2 b. The same elements as in FIG. 2 a are provided in the system labeled 200, but in FIG. 2 b for the sake of clarity the activating connections 311, 312 and the regulating device 31 have not been shown. The regulating device 32 shown in FIG. 2 b is connected initially to the motor M via an activating connection 321 and to the brake B (of each drive unit 22) via an activating connection 322. However, according to the invention other activating connections 331 and 332 are also provided with switching means S, associated with the latter, in the form of contactor circuits. The switching means S can, for example, take the form of power switches. A connection can be made between the regulating device 32 and the drive unit 21 by the switching means S so that the drive units 21 and 22 can be activated in parallel by the regulating device 32. To do this, another activating connection 340 is provided that enables the motor phases and the braking circuit to be switched synchronously. The switching means S can thus be switched either in accordance with a superordinate control system that detects a fault in a regulating device 31 and/or by a reciprocal monitoring of the regulating devices.

A flow diagram of a method according to a preferred embodiment is shown in FIG. 3 and labeled 300 as a whole. The method is imoplemented when malfunction of a regulating device 31, 32 is detected in a step 301. The detection takes place, for example, using signals 310, 320 supplied by the regulating devices 31, 32 or on the basis of a signal 90 from a superordinate unit 9 connected to the regulating devices 31, 32 via connections 8.

After a malfunction has been detected in step 301, switching means S are activated S′ in step 302, as a result of which, as explained above, drive units 21, 22 can be activated in parallel by a single regulating device 31, 32.

After step 302 is complete, a parallel simultaneous activation of activating units 21, 22 is thus effected. If asynchronous motors M are used, for example, in the activating units 21, 22, it can be advantageous to permanently monitor an angular position M′ of the motors M in a step 303 and optionally initiate a synchronization step 304, as explained above. If other means are available for ensuring the symmetry of the angular positions, to simplify matters steps 303 and 304 can be omitted.

The method according to the invention continues with parallel activation until, in a step 305, for example because of maintenance, normal operation of the 

1. A system for altering the pitch of rotor blades of a wind turbine, comprising: a plurality of drive units, each drive unit of the plurality of drive units being individually associated with each of the rotor blades; a plurality of regulating devices, each regulating device of the plurality of regulating devices being individually associated with each drive unit of the plurality of drive units; and a plurality of activating connections, each activating connection of the plurality of activating connections being switchable by means of switching means, wherein via the plurality of activating connections, in the event of a failure or a malfunction of at least one regulating device, a drive unit associated with the at least one regulating device is activated in parallel and simultaneously with another drive unit with a regulating device associated with the other drive units.
 2. The system as claimed in claim 1, wherein each drive unit of the plurality of drive units has an electromotor and a braking device that are connectable by the switching means simultaneously to the regulating device associated with the other drive units and is disconnectable from the regulating device associated with the other drive units.
 3. The system as claimed in claim 1, wherein each drive unit of the plurality of drive units has an electromotor in the form of an asynchronous motor.
 4. The system as claimed in claim 1, wherein each drive unit of the plurality of drive units has an electromotor in the form of a synchronous motor.
 5. The system as claimed in claim 1, wherein at least one drive unit of the plurality of drive units has a position sensor.
 6. The system as claimed in claim 5, further comprising: a further regulating device configured to activate the at least one drive unit can be effected in parallel with the other drive unit with the regulating device associated with the other drive unit.
 7. A method for altering the pitch of rotor blades of a wind turbine with a system having drive units individually associated with each of the rotor blades, regulating devices individually associated with each of the drive units, and activating connections that are switchable by means of switching means, comprising: activating a drive unit in parallel and simultaneously with another drive unit with a regulating device associated with the another drive unit in the event of failure or a malfunction of at least one other regulating device.
 8. The method as claimed in claim 7, further comprising: determining the pitches of the rotor blades and synchronizing the pitches by decelerating and/or adjusting motors of the drive units associated with the rotor blades.
 9. The method as claimed in claim 7, further comprising: reducing an activating power of the motor, when a critical rotor displacement angle of at least one motor of a drive unit is exceeded, wherein the at least one motor is a synchronous motor, and wherein the at least one motor is associated with one of the rotor blades.
 10. The method as claimed in claim 9, in which further comprising: (i) determining a mechanical angle of the motor, (ii) calculating an angle of a related electrical field, and (iii) comparing the mechanical angle with the angle of the electrical field in order to determine a rotor displacement angle of the at least one motor. 